1. Field of the Invention
This invention relates to an integrated circuit package structure and a method for the same, especially relates to the integrated circuit package without a solder mask and the method for the same to increase a circuit density and the reliability of the integrated circuit package.
2. Description of the Prior Art
Integrated circuits are typically housed within a plastic package, for example a quad flat pack (QFP). Flat packs contain a lead frame, which has a plurality of leads that are connected to an integrated circuit die. The die is encapsulated by a hard plastic housing, which mechanically supports and electrically insulates the integrated circuit. The leads are typically soldered to a printed circuit board.
Packaging techniques for integrated circuits have been developed in the past in an attempt to satisfy demands for miniaturization in the integrated circuit industry. Improved methods for miniaturization of integrated circuits enabling the integration of millions of transistor circuit elements into single integrated silicon embodied circuits, or chips, have resulted in an increased emphasis on methods to package these circuits with space efficiency.
Integrated circuits are manufactured from a silicon wafer using various etching, doping, depositing and cutting steps that are well know in the art of fabricating integrated circuit devices. A silicon wafer may be comprised of a number of integrated circuit dies that each represents a single integrated circuit chip. Ultimately, transfer molding plastic encasement around the chip with a variety of pin-out or mounting and interconnection schemes may package the chip. For example, M-Dip (Dual-In-Line-Plastic) provides a relatively flat, molded package having dual parallel rows of leads extending from the bottom for through-hole connection and mounting to an underlying printed circuit board. More compact integrated circuits allowing greater density on a printed circuit board are the SIP (Single-In-Line-Plastic), and SOJ (Small Outline J-leaded) molded case packages.
According to numbers of chips in the integrated circuit packages, the integrated circuit packages can be divided into a single chip package (SCP) type and a multichip package (MCP) type. The multichip package type also comprises a multichip module (MCM) type. According to a type for coupling a substrate and an element, the integrated circuit packages can be divided into a pin-through-hole (PTH) type and a surface mount technology (SMT) type. A lead frame of the pin-through-hole type element is thin acicular or a sheet metal to be inserted into a socket or a via of the substrate and to be fixed by using soldering process. The surface mount technology type element is adhered directly on the substrate and then is fixed by using a soldering process. At present, the more advanced process for packaging integrated circuits is a direct chip attached (DCA) packaging process to decrease the volume of an integrated circuit package and to increase the circuit density on the inside of the integrated circuit package. The direct chip attached packaging process is to fix the integrated circuit chip on the substrate directly and then to couple the circuit elements with each other.
Referring to FIG. 1, this shows a diagram in fixing a chip on a substrate with a solder mask. At first, a substrate 10 and a chip 40 is provided, wherein the substrate comprises a plurality of layout circuit leading wires 25, a plurality of the first solder pads 20, solder mask 30, and a pre-soldering 18 (can be omitted following needs of products and processes). The chip 40 comprises a plurality of the second solder pads 45 and a plurality of solder bumps 15. The plural solder bumps 15 are coupled to the chip 40 by using the plural second solder pads 45. Then chip 40 is coupled to the plural first solder pads 20 or pre-soldering 18, which is on the substrate 10. By using the plural solder bumps 15 to fix chip 40 on substrate 10, wherein a location of each of the solder bumps 15 is corresponding to each of the first solder pads 20.
In the traditional integrated circuit package, the objective using solder mask 30, is to avoid the layout circuit leading wires 25, on substrate 10, from outside environmental damage, and to prevent a short circuit because of overflow of the solder bumps 15 in the following process. Therefore, in the traditional integrated circuit package with a solder mask, the solder mask 30 must be covered on the layout circuit leading wires 25 to prevent the layout circuit leading wires 25 on the substrate 10. In order to provide better protective capabilities, the solder mask 30 must be further covered partially on each first solder pad 20 on substrate 10 to avoid a short circuit because of the overflow of solder bumps 15 in the following process. Because a solder mask 30 must be covered partially on each first solder pad 20 of substrate 10, an extra boundary around each first solder pad 20 must be reserved to connect the solder bump with enough allowance and tolerance in the traditional integrated circuit package with a solder mask. Because of the extra boundary, the numbers of circuit leading wires, which are located between any of the two first solder pad 20's on substrate 10, will be decreased and the volume of the integrated circuit package with solder masks will not be successfully reduced. Therefore, the traditional technology is not used in the integrated circuit package whose volume suitability has becomes smaller and smaller.
Because the solder mask must be covered partially on each first solder pad in the integrated circuit package with solder mask, the misalignment in the solder bump location will affect the quality of the integrated circuit package when the solder bump is coupled to the first solder pad. When the substrate comprises more circuit layers, the solder mask will not be filled in the needed location and will in affect have short circuit defects. When the flip chip (FC) type, which means not all of the integrated circuits are covered with the mounding compound, is used to package the integrated circuit or the combination ability between the solder mask and the underfill is less, the solder mask will come off the circuit leading wire to cause a lower reliability and short circuit defects.